The invention is directed to a plate type rotational separator and a method for separating one or more components from a fluid (gas, liquid or combinations thereof) stream.
Devices for separating components from a fluid (gas, liquid or combinations thereof) are known in the art. One sort of separating devices separates different fluids and/or solids from fluids or droplets or particles from gases by a difference in specific gravity. For instance in settlers, this kind of separation technique is applied by using gravity as the driving force. For certain applications, where small particles or droplets are dispersed in a fluid or gas, gravity is not sufficient to separate the different phases. To enhance separation, the centrifugal force is used. For instance in the milk industry, to separate fat particles from whole milk, centrifuges are found to be suitable separators. Due to their high rotational speeds, these devices can reach centrifugal accelerations that are several orders of magnitudes higher than the gravitational acceleration. This results in that the separation velocity is very high and the separation very efficient. In order to further increase the efficiency of these centrifuges, they are often provided with internals. These internals increase the efficiency by preventing turbulence and increasing the effective surface area. The most frequently used internals are plates in different shapes and sizes.
Robert Plat describes in his PhD thesis “Gravitational and centrifugal oil-water separators with plate pack internals”, Delft University of Technology, 1994 (ISBN:90-6275-985-8), among other separation techniques, plate packed centrifuges containing different geometrical arrangements of packs of plates. A specific geometry that is described by Plat in more detail is a set of plates arranged parallel to the axis of rotation. The plates in these centrifuges are positioned at an angle relative to the radius.
An advantage of this device is that the flow direction of the contaminated fluid feed is parallel, or substantially parallel, to the rotation shaft. As a result, there is no or negligible counter flow of contaminated fluid. Such counter flow is for instance one of the disadvantages of a stacked disk centrifuge system such as described in Appendix D of the PhD thesis of Plat. The absence of a counter flow of contaminated fluid makes the device less dependent on the feed flow, on the different densities of the components, and on the different viscosities of the components.
With radial plates the plate distance increases towards the outer radius. Droplets entering the pack near the outer radius have to travel a longer distance to reach the surface of a plate than droplets entering the pack near the inner radius. Since the continuous-phase flow velocity increases with plate distance, the liquid which enters the plate pack near the outer radius will have a relatively low residence time. Together with the longer settling distance, this will negatively affect the separation efficiency near the outer radius. Plat therefore suggests using curved plates instead of flat plates, thereby making the plates more or less equidistant.
A major disadvantage of the device described by Plat is that it is very difficult to clean, in particular to remove any deposited solids from the plate pack. Cleaning the plate packs is difficult because of the relatively small distance between the plates and the curved shape of the plates. The curved shape makes it difficult to enter the space between the plates with scrapers in a direction other than in the direction of the axis of rotation of the plate pack. Plat acknowledges this disadvantage in his thesis by stating that plugging of plate packs by scale is often a problem, in particular in food industry, because of hygienic aspects. It would be desirable to have a device with comparable or even better separation efficiency which would be easy to clean.
Moreover it is disadvantageous in that a complex procedure is needed in this device to isolate a valuable heavy component.
Another type of separation device is presented in GB-A-1 476 670, which discloses a separator having an inner carrier with radial vanes attached thereto. The inner carrier and the vanes are rotatably mounted in an outer shell, which can be rotated independently of the vanes and the inner carrier. During separation the outer shell is rotated, the liquid entering the separator is rotated as well by the rotating action of the outer shell. This rotating action of the liquid entrains the inner carrier and the vanes. Thus, during normal operation the inner carrier is rotating at approximately the same speed as the outer shell. When the apparatus needs cleaning, the motion of the inner carrier is suddenly stopped by a brake. By this braking action, the vanes will wipe along the inner side of the outer shell, thus generating turbulence. This turbulence will loosen any clogging that had taken place on the inside of the outer shell. However material clogging to the vanes themselves is not affected by this operation, which is a drawback of this apparatus.
A further disadvantage of the apparatus of GB-A-1 476 670 is the complex sealing of the rotating outer and inner members. A further disadvantage is that the clogging on the vanes is difficult to remove. If the fixed mass is the valuable and recoverable mass, this apparatus is not suitable since it needs the liquid phase in order to remove the solid phase.
A further separation apparatus is presented in WO-A-99/54021. This document discloses a rotary type of separator with a set of disc shaped stacked flexible plates. In order to clean the plates, the separator is hold still. Due to the gravitational force, the separator plates are flexing downwards and thereby rub against each other. This rubbing action is disclosed to be sufficient in order to clean the plates.
A disadvantage of this separation apparatus is that it renders reclaiming the solid mass from the separator extremely difficult. A further disadvantage is that the flexible plates can stick to each other when the apparatus is out of service.
Another separating apparatus is presented in SU-A-1 369 810. This separation apparatus is provided with a first carrier to which curved flexible separation plates are attached. The separator plates are reaching through slits in a cup which can be rotated under a predetermined angle with respect to the first carrier. By rotating the cup, the slits move relatively to the carrier and thus slide along the surface of the plates. This exerts a cleaning action upon the plates which are wiped clean.
Again this apparatus is less suitable for reclaiming the solid mass from the separator. With this wiping and cleaning action again the liquid phase is needed for cleaning, thus re-diluting the valuable solids. A further disadvantage of the wiping cup is that the plates cannot be supplied with spacers or caulks, since these would obstruct the sliding of the plates within the slits of the wiping cup. Without the spacers, at high rotational speeds the flexible plates can deform, thus deteriorating a good separation performance.
Object of the present invention is thus to improve the separators known in the art as described above.